Organised criminals in the UK may be buying powerful machine guns and other weapons from the Balkans that have been made or stolen to order, a BBC investigation reveals.

In November last year, suspicious customs officers at Dover pulled over a Croatian registered truck carrying a shipment of frozen pizzas.

An X-ray inspection of the truck's spare wheel revealed a much more sinister cargo: 30 sub-machine guns, along with silencers and ammunition.

In addition, the BBC's Correspondent programme has since discovered that the weapons were not marked with serial numbers, making them untraceable.

We are alive to the fact that we are likely to make more seizures like this

Ian Watson, HM Customs

This suggests either a manufacturing process geared deliberately towards illegal trafficking, or that the guns had been stolen to order from a production line before serial numbers were added.

In the court case that followed the Croatian driver was found not guilty of any wrongdoing.

This case, and three other similar seizures in the last year by HM Customs, highlight a worrying development in global arms trafficking, with weapons of war now ending up on the streets of western Europe.

Ian Watson, of HM Customs, told the programme: "We are alive to the fact that we are likely to make more seizures like this.

"If they've been coming in now, the chances are we are going to find more in the future."

One senior unnamed source from a European police force also told the BBC: "A shipment like that would have been owned by an organisation, by a criminal structure.

HM Customs and Excise can check any cargo entering the country

"You don't buy that quantity of weaponry on spec. And 30 unmarked weapons like that were not destined for individuals."

The guns have since been identified as the Croatian manufactured "Mini-Ero" 9mm sub-machine pistol, itself a copy of Israel's world famous Uzi.

This type of weapon is a favourite with criminal organisations the world over because it is so small.

It can be concealed under a jacket, but with a cyclical fire-rate of over 1,000 rounds a minute it also packs massive firepower.

Fears for future

The programme investigates how the end of the Balkan wars in the late 1990s has led to a massive rise in the illegal sale of weapons.

Despite the fact that Croatia had no indigenous small arms industry of its own before the Yugoslav civil war, it became adept at copying other countries' designs and manufacturing light weapons to a very high standard.

Any alliance between indigenous UK criminals and Balkan mafias could be disastrous

Anonymous UK police intelligence source

Weapons from the Balkans entering the UK in this way still account for a small proportion of the total number of guns in this country.

But the British police fear that many Balkan manufactured weapons are now being sold on the criminal black market, as individuals with links to the wartime military-industrial complex seek out new markets for these guns now the fighting is over.

"Criminals in well policed societies like Britain don't have much use for bigger weapons like Kalashnikov assault rifles, as they are so hard to conceal.

"So generally handguns are still the weapon of choice", said one UK police intelligence source on condition of anonymity.

"But seizures like this are very disquieting. It could be that some of the newly arrived criminal groups are starting to get organised in this country.

"The question is, are they arming themselves or do they plan to sell these weapons on?

"Any alliance between indigenous UK criminals and Balkan mafias could be disastrous."